1. Field of the Invention
The present invention relates to a holder for the illuminated end of a bundle of optic fibers for light emission, e.g., for illumination in "star ceilings".
2. Description of Related Art
For optimal use of a common light source for this purpose, it is usual to employ a reflector lamp, the parabolic reflector of which acts for collecting of the light, i.e., emits the light inwardly towards a focal point or area located reasonably shortly in front of the reflector and the lamp. The optic fibers typically have a thickness of about 1 mm, and if only one or rather few fibers were used, their input ends could well be located just in this focal point. However, it is more usual to employ some 50-300 fibers which, at their input ends are held together in a tight bundle, by means of a holder for insertion in a holding socket of a lamp housing near the said focal point. In order to ensure that the whole of the end surface of this thicker fiber bundle is effectively illuminated, this end is placed not in the focal point, but spaced such a distance in front of this point that the light at this place, after having passed the focal point, has started to be spread again, viz. to such an extent that it will illuminate an area just corresponding to the area of the end of the fiber bundle. Thus, a high efficiency is achieved by a combination of two features, viz. the tight juxtaposition of parallel fiber ends and a well controlled axial positioning of the end surface of the bundle, all according the area size thereof.
It has been possible to take advantage of this combination in connection with differently sized holders for the ends of fiber bundles of different sizes, viz. in that holders for fiber bundles of respective thicknesses may comprise holder bushings adapted both thicknesswise and lengthwise to different bundle thicknesses, e.g., with jumps of 50 fibers.
It will thus be a possibility that a main portion of a holder may optionally be connected with different holder bushings which will then, when the main portion is inserted in a receiver socket in the lamp housing, automatically determine the correct axial position of the fiber ends, when these are cut in plane with the free outer end of the holder bushing.
However, a structurally simplified solution has already been proposed, viz. the use of a holder having an internal passage of such a conical shape which precisely corresponds to the conic envelope of the light beam, see U.S. Pat. No. 5,341,275. Hereby, a fiber bundle of any size between a given minimum and maximum will be introduceable into the holder for automatic achievement of a correct positioning of the end surface of the fiber cable in the holder, which may thus, after the mounting of the fiber cable therein, be inserted into a fixed position in a suitable fixture. From an immediate point of view, this will appear as the simplest possible solution, but it is connected with a practically very important drawback, viz. that the end surface of the fiber cable shall have to be finely worked prior to the fixation of the cable end in the holder. Typically, this fine working comprises a plane grinding and fine filing operation on the cable end, while the fixation is most efficiently effected by means of a gluing or joining substance. It has been found difficult to avoid that such a substance, by the said fixation, penetrates out through the end surface, whereby the effect of an already worked out fine finish will be more or less destroyed.